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Could an explosive decompression trigger the smoke detectors?
In a commercial airliner at FL370, in the event of rapid (explosive) decompression, will the cabin air fog? And can that fog trip smoke detectors?
Pressurized aircraft can have a cabin altitude of 6,000 ft, or so. What is the differential pressure at 37,000 ft? Again, would an explosive decompression of 8-9 PSI, fog the interior environment?

It would probably fog,  but not long enough to trip any detectors even if they would alarm on condensation, which is doubtful. Same reason your smoke detector in your house wouldn't go off if you held it above a pot of boiling water in the "fog".

lower pressure could cause overheating for air-cooled components

Explosive decompression would require the loss of a door-sized piece of the fuselage. Surely the smoke detectors going off would be the last thing you would be concerned about, and that's assuming you can even hear it over the outrush and then wind noise.

If the cargo fire detectors went off, that WOULD get the pilots' attention, as well as needlessly complicating the troubleshooting process. Never heard of that happening, though. Maybe even because of engineering so that the detectors reject exactly this sort of "false positive" indication.

@RonBeyer That all depends.  If I have a long hot shower and open the bathroom door before the extractor fan has dealt with most of the steam, it sets my smoke alarm off.

@Simon I don't doubt it, although I've never had that problem. The industrial ones are much better than what you have in your home though, as part of my job I interface with Siemens fire systems regularly and I've been on commercial vessels that misted the entire engine room without setting off a fire alarm.

Does the smoke detectors turn on the sprinklers in case of a smoke / fire?

@Firee the cargo hold or APU compartment may have a co2 system but I don't know any aircraft that has a built in water or AFFF system.

@RonBeyer Why no water sprinkler? CO2 can have adverse effects of living beings.

The amount of water you would have to carry would halve the carrying capacity of the aircraft. Combined with weight of plumbing and possible electrical shorts the better option is nothing at all. I mean at that point it may be more economical to have passenger ejection seats... also note that the APU compartment or cargo hold doesn't vent into the passenger space.

@Firee: Sprinklers? FAA study (2001): "Currently,  commercial  transport  cargo
compartments are protected with Halon 1301 fire suppression systems.  Water spray is being considered as an alternative agent
for  Halon  1301  which  is  no  longer  being  produced  because  of  its  ozone  depletion  potential"

In an explosive decompression the cabin air may fog, this is because of rapid cooling causing the moisture in the air to condense. How thick it is and how long it may last depends on a number of factors.
There are two types of smoke detectors, these are optical particle detection devices and ionization devices. Both types are used on commercial aircraft, some detectors have both methods built in.  Ionization devices are tripped by changes in the electrical conductivity of the air flowing through them and are not very sensitive to steam. Optical smoke detectors work on a different principle, detecting light being scattered by particles in the air. Optical devices are susceptible to false readings from moisture, in fact manufacturers of home devices recommend they are installed away from bathrooms to avoid false alarms.
However, airplane certified units are designed and built to a very high standard, the FAA states in the Aviation Maintenance Handbook that requirements for fire protection systems include:

No false warnings under any flight or ground condition.

So it is very likely that the manufacturers have taken steam into account, after all cabins sometimes fill with steam when the air conditioning has been turned on when if the air is very moist. An extreme example is this flight at Shenzen. That did not set off smoke alarms, and although I've never seen it that bad I have personally been in the cabin when it's noticeably filled with steam and there were no smoke alarms.
So yes, the cabin can fill with steam in an explosive decompression, but it is unlikely - but possible - that the smoke alarms would go off.

False warnings can and do happen, and are sometimes associated with high moisture cargo. Ultimately it's better for the sensors to provide a false warning rather than miss a real fire.


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Is Naproxen (medication) approved for flight?
Is Naproxen an approved FAA medication? I have found 2 separate websites which comment on this type of medication that seem to be somewhat ambiguous, at least to the degree that I'm looking for.

https://www.faa.gov/about/office_org/headquarters_offices/avs/offices/aam/ame/guide/pharm/dni_dnf/
https://www.leftseat.com/medcat1.htm

Is there a singular location to find out if a medication is approved or not approved? Specifically I'm looking for Naproxen.

It is approved on a case-by-case basis, so you would have to go through your medical examiner to get this submitted for approval.

Naproxen does not fall under any of the categories listed on the FAA page as grounding the person taking it. On your other (non-official list) it's said to be ok unless you're precluded from flying by side effects or by the condition for which you're taking it.

There's no fully authoritative source for this information, other than consulting an AME directly. AOPA's medication database is considered pretty reliable (and it says Naproxen is allowed) but their generic disclaimer explains why you can't just look up a medication in a list:

Although these medications are generally allowed by the FAA for flight
  duties, there are variables with each individual's situation that
  could render a particular medication inappropriate for flying because
  of case history or adverse side effects. Some medications are being
  used "off label". This means that a drug is prescribed for symptoms
  that do not fall within the FDA's approval guidelines for that drug.
  This is just one example of why the FAA might not approve a drug that
  is on the list.

In other words, as with all medical questions you have to consult a  professional to get the right answer for your personal situation.

For the sake of curiosity, what if one were to strictly go off the medical database  for approved medication and not consult an AME? There are all kinds of medication and I would think it could make it prohibitive at times to contact an AME for every type of medication that one might need to take (tylenol, ibuprofen, etc.) every time they might need to take it.

First off (until all the third class medical reform is in place) you still need to get a Medical exam to fly and you need to report all recurring medications. As for one off medications and over the counter things you, as PIC need to decide how it effects you and if it will negatively impact your flight. If you are concerned in any way, contact an AME.

@RyanGriffith I don't think anyone cares about 'typical' OTC stuff if you're just taking it for a day or two and you know there are no side effects. You're expected to evaluate your own fitness before every flight anyway. But if you start taking any medication regularly, or you get a new prescription for something, then checking with your AME would be a good idea.

The reason it is approved case-by-case is because the AME may need to verify the condition, not the medication. For example if you take it for chronic knee pain, the AME may want to verify that you have full range of motion and adequate strength in your knees from a sitting position.

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Is a weak battery a valid reason to reject a rented aircraft?
Today I had rented a Piper Archer III for a local flight. After taxing to the fuel and filling up, I went to start the plane again and it did not want to turn over. This particular plane is somewhat fussy and sometimes doesn't start right away. As I continued to crank the engine over, you could tell the cranking lulled and the battery was having difficulty turning the engine over as effortlessly as it typically would. At one point the prop wouldn't even rotate.
I eventually got the plane started after a series of cranking / resting periods. I made the decision to not fly given the battery issue and returned the plane to its hangar.
The owner of the flight school was initially reluctant to comp the 1/3 of an hour I had on the hobbs (from taxing to gas pumps, etc) stating that once I had the plane started, I could have flown since it would have been powered by the magnetos.
My question: I know that the plane is powered by the magnetos once started, however, was my decision to not fly unfounded and unnecessarily cautious or would there be good reason not to fly knowing that the battery was weak and unreliable?
Update: It seems that some answers and comments have a focus on the financial aspect of my question. To be clear, this is not about money or how much. No one should pay for goods or services that were not rendered. The FBO's argument was that the choice not to fly was my own and not due to a responsibility of the FBO's to fix a "broken" plane. The money aspect is just an indicator of where the responsibility lies, on my shoulders or the FBO's.

While it’s not necessarily unsafe in VFR conditions, it’s never a good idea to take off with some degraded system. What if the alternator failed or the alternator wire broke? It happened to me before and I took off not knowing it or recognizing it. 15 mins into the flight avionics started shutting down. No fun. I would have aborted too and the owner is potentially suggesting bad airmanship if saying you should have flown. That said, the financial aspect is another matter between you and him.

How much time was spent cranking? Did you perform a hot start or attempt a normal start? The owner may be very experienced and knows that the flight would have been safe, hence his frustration. That said, you were PIC and made the safe decision.

agree. the magnetos do not power the avionics nor the nav, interior, or landing lights. You did the right thing. If the plane had a chronic warm start issue, the owner should have gotten that fixed or at the very least warned you about it.

Is "battery" on the aircraft's Minimum Equipment List?  It's on my car's. Also, are you in the Northern Hemisphere?

I wouldn't even do this in a car, for goodness sake!

If the battery wasn't charged there's a possibility, depending on the electrical design of the aircraft, that the magnetos themselves were fried which could have been catastrophic depending on which stage of the flight the battery became unable to keep a spark. I had this problem with my old motorcycle.
Here's an exact quote from the manufacturer's preflight checklist for that aircraft, "DO NOT ATTEMPT FLIGHT IF THERE IS NO INDICATION OF ALTERNATOR OUTPUT".  A dead battery is the strongest sign of no alternator output.

@NoahWood your comment doesn't make much sense in the context of a light aircraft electrical system. The ignition system (magnetos) is entirely unrelated to the battery/alternator. It is true that a weak battery can be a sign of a weak alternator, but that's hardly catastrophic for a VFR flight. "battery unable to keep a spark" is nonsensical for a magneto-based ignition system.

First off, you absolutely made the correct decision. As PIC/pilot you have not only the ability, but the duty to call off any flight you don't feel comfortable regardless of the reason. Your go/no go decision can be based off of anything and you should always be comfortable making that decision.
Now as far as the battery goes I can tell you I was in exactly this situation a couple years ago with a rented Piper Comanche. It was cold out and the start attempts completely killed the battery. The FBO (also the owner) decided to jump it using a start cart and got it going. They comp'd me about .25 hours since they wanted me to sit on the tarmac at 1200 RPM until the oil temp gauge came up (something that I would have done anyway).
I made the decision to go, but I also made (a rather poor) decision to board a passenger while the aircraft was running (at the direction of the FBO and because I was at an unattended airport to pick that passenger up). I don't regret taking the aircraft but I never felt comfortable boarding somebody with the engine running.
In this situation you probably would have been fine had you left, provided you were making a VFR flight in good conditions. If this were IFR I would say that it would be better to say "no-go". The only thing you would probably have noticed would have been the ammeter showing the battery charging, but it would probably have recharged the battery in about 30-45 minutes of flying.
The other question is if the owner should have comp'd you for this and that is a little harder. You probably didn't burn all that much fuel or put much time on the engine tach so I'm guessing that while it would have been inconvenient to the owner, you didn't make a lot of difference financially (maybe $20 at most).

+1 for "As PIC/pilot you have not only the ability, but the duty to call off any flight you don't feel comfortable regardless of the reason" alone.  It'd be crazy IMO if the person actually piloting the plane (and thus in charge of their life, and their passengers' lives) didn't have last call on whether to take a metal tube, with some wings and engines strapped to it, up into the sky hundreds/thousands of feet above the Earth.

What @BruceWayne said.

Since no one seemed to diagnose the actual problem—alternator, charging system, or battery—the wisest course is a no-go.  If the battery has expired, no amount of engine running will charge it.  Also, it could destroy the alternator if the battery's failure mode included an internal short.  This sets up a potential chain of failure where the avionics, lights, and electric flaps are inoperable.  Night?  Short runway?  No way to broadcast MayDay?   (Bold pilots don't become old pilots.)

I'm impressed you got comp'd.  I've made it all the way to runup to find the carb heat was bad (arm snapped off) and didn't even get comp'd!

@BrianKnoblauch Another contributing factor is that I called the FBO for a preheat and they did not do that, they forgot then told me to just "run it", which killed the battery when I tried to start. I knew it wasn't going to start, it was around 20°F outside.

Before I answer its pertinent to clarify something as your wording it a bit tricky,

I know that the plane is powered by the magnetos once started

The spark plugs are driven by the magnetos, the airplane (electronics etc) is powered by the alternator/battery once started. This is important as you can have a running engine with both a faulty battery and a faulty alternator. Its also worth noting that in the event of a battery too weak to crank the engine you can even hand prop the aircraft to get it running which, once running (provided there is some juice to run the alternator fields) will recharge the battery.
On to the topic at hand;

As I continued to crank the engine over, you could tell the cranking
  lulled and the battery was having difficulty turning the engine over
  as effortlessly as it typically would.

This makes it sound like you killed the battery (or at least it was on its way to dead). A battery's ability to crank an aircraft, diminishes as you use up the stored energy. In your case, if the plane was started and running, while the ammeter was registering 0 or +amp current, then you are good to fly. However, it may be a good idea to idle on the ground a bit and recharge the battery some prior to takeoff to avoid high alternator draw on takeoff and climb out.
If the battery was good for "a series of crank/rest periods" than I would not consider it weak and unreliable.
NOTE: If you are concerned or feel uncomfortable you should never make a flight and you should report any and all things to the owner of the aircraft.

Couple of nits to pick:  "The spark plugs are driven by the magnetos once started".  The spark plugs are always driven by the magnetos and the magnetos are driven by the rotation of the engine.  "Its also worth noting that in the event of a dead battery you can even hand prop the aircraft to get it running which, once running will recharge the battery."  This may work if the battery is too weak to crank the engine, but not if the battery is totally dead.  The alternator requires some voltage to set up the field and output power.

@Brian I have edited the verbiage on the magnetos and alternator to reflect.

@Brian, is the charging system different from a car? A car can certainly charge a completely dead battery after a push start.

@prl There's won't start the car discharged (usually around 80%) and completely discharged (aka "deeply discharged"). Most times the car battery doesn't get to the second state, because most people know to stop discharging it as soon as it won't start the car. But if you sit there cranking on the starter even after you clearly have a discharged batter, you can really mess it up.

You can't push start cars anymore on dead batteries because they have too many electrical loads required to work fuel and spark.  When the battery is too low to safely crank, the starter solenoid will drop out and disconnect the starter. At best you will get many clicks, but not for much longer.

is my decision to not fly unfounded or would there be good reason not to fly knowing that the battery was weak and unreliable?

A weak battery does not generally pose a problem to an electrical system - even if it presents a constant load, the alternator should be more than powerful enough to maintain that load as well as all other electrical loads.
The problem with a weak battery is that it may be a symptom of a more significant problem.  If it suggests a failing alternator, bad voltage regulator, or some other issue then it's possible you may experience a mid flight electrical failure.
If it's simply an older battery, it's cold, or it was recently started and stopped without allowing the battery to fully recover from the starting procedure then there may not be any reason to abort the flight as these issues are temporary in nature and do not reflect poorly on the safety of the plane.
However, if the battery failure is due to some other electrical system problem that could disable the electrical system during flight then you have two issues depending on the engine type:
Magneto engine with no engine computer or fuel injection
If the engine does not use fuel injection or an engine computer, and has magneto(s) for spark then it will remain running even without the alternator or electrical system.
In this case, you may lose some or all of your electronic avionics if the electrical system fails.  However you should still be able to maintain control of the plane.
Engine with computer, fuel injection, or electronic ignition
If the engine has a computer, has fuel injection, or uses an electronic ignition system (ie, non magneto), then it's possible you'll lose engine power if the electrical system fails.
In other words, if the engine requires power to correctly operate or you require power to correctly fly (for instance needing electronic instruments for IFR conditions) then you should be very careful about flying a plane which is showing any problem with the electrical system.
Understand your electrical system and how to deal with emergencies
You need to understand at least in a basic manner how your plane is wired, and how to operate the breakers correctly in case of electrical failure.  You need to understand what redundancy is available in the electrical system, and how to verify that all redundant options are correctly operating.
It may well be that this has already been drilled into you through training on this model of aircraft - when X happens, do Y - but a deeper understanding of the reasons behind taking certain actions when certain alerts occur will help you understand if a weak battery is cause for concern.  If your engine has two alternators, if your avionics have multiple battery backups, if you have two power buses and two batteries - all these things can provide confidence that the aircraft will operate well despite having difficulty starting.  If the aircraft has none of these, or if you aren't sure, or you don't know how to test or check these systems, then you should probably avoid flight until you've corrected the issue, or learned more about the aircraft.

+1 for detailing the actual risks of overall failure. I'm amazed none of the other answers bothered to try.

One caveat: VFR with no electrics is OK, but I would really not want to be IFR without an electrical system, especially on a plane with a glass cockpit!

@UnrecognizedFallingObject Modern glass cockpits have multiple power buses and multiple power backups so the reality is that even if one bus completely fails you'll still have critical avionics. That said, if you're asking questions like, "Does a weak battery constitute reason to scrub a flight?" then you likely don't know the plane well enough to understand what level of redundancy it has, and how to verify that all the parts of the redundant systems are operating correctly.

Interestingly this is pretty similar to what's required of astronauts. They may not fully grok the difference between Windows and Linux, but they are trained and have manuals that they can use to completely re-install the OSes that drive the ISS (when X happens, do Y).

@WayneWerner Yes, in fact they're trained not to think about the problem, but to simply act according to the emergency training and procedures. Thinking not only slows things down, but introduces possible mistakes, and in the air or in space you generally don't have time to figure out the root cause.  This isn't unusual to these two areas either, emergency medical technicians have a similar approach.

That's kind of interesting - I hadn't put 2 and 2 together there, but it makes sense. It also makes sense on a more personal level - talking about needles and blood and cuts gives me the absolute weebles. However, over the year my children have had fairly intensive injuries - cut eyebrow falling off a bike, another bit his tongue, another got some adult-level scissors at a birthday party and cut her hand enough to require stitches. Each time I simply acted according to the Scout and Red Cross training I'd been given - not a single weeble experienced.

If you're unsure of safety for any reason, "no-go" is generally the right choice.  If it turns out later you didn't need to be so conservative, that's fine and you can always do it differently next time - what matters is your assessment of the situation at the time.  Of course, you are correct that the magnetos will keep the engine running no matter what happens with the rest of the electrical system.  The question is what's going to happen there, and how much it matters.
I would have no reservations at all making a "go" decision here for a VFR flight (or an IFR flight in VFR conditions), which I have done uneventfully three times.  I would only go if there's a jump available, though - hand propping is definitely a no go for me!
IFR is a little different.  It's not an absolute no-go (fully-charged battery is not on the list of required IFR equipment!)  If the weather is below VFR minimums, you have a slightly larger (though still small) chance of needing to navigate in IMC without your electronics and having to do lost-comm procedures.  If that's not OK, stay on the ground in IMC.  For me, this would depend on exactly the situation with the weather.  I might also want extra fuel reserves.  But this would probably push me into "no-go" territory only if the flight was pretty marginal to begin with.
The power for the electrical system is primarily provided by the alternator.  The purpose of the battery is to supply power for starting and to smooth out electrical current - its ability to power instruments is secondary.  Once you eventually get the engine started somehow, your battery should recharge fairly quickly IF the alternator is working.  Check your ammeter - if the ammeter shows negative or zero charge, you're likely to have an electrical failure and should not fly unless you are prepared to have no electronics for most of the flight.  Dead alternators are a common cause of dead batteries, so don't forget to check this!
But if the ammeter shows a positive charge, you're very likely to be fine because the alternator, not the battery, is the important piece of this puzzle.  If you have a glass panel or an electronically controlled engine, there's a decent chance you have a dual electrical system to go with it - in that case, you're in better shape with a dead battery than you would be with one alternator and a brand new battery, and nobody would think twice about that!
The bottom line is that electrical systems do fail, and a discharged (but working) battery doesn't really increase the chance of this happening.  At most, it reduces the time you have from alternator failure to loss of electrical power.  But this doesn't matter as much as you might think it does.  Three of the four electrical system failures I've had, counting both aircraft and cars, caught me completely by surprise.  One was a dead alternator that I simply didn't notice (did you know a discharging battery is only about a needle's width on the ammeter different from a fully charged one?  You will only even notice it if you are pretty familiar with the plane and look closely), another was a dead alternator in a car that didn't have an ammeter, and the third was a wiring failure that happened so suddenly that I couldn't have done anything about it anyway.  Only one of the four did I spot before it became a problem by using the instrument cluster.

Every car I've had (which, admittedly, isn't that many) has had an indicator light for "generator failure". You don't really need an ammeter (though it might be nice to have), all you need is to know whether there's a drain on the battery during normal operations.

Oh, it had the light.  If only it had another light, to indicate the failure of the alternator failure light! :)

"If only it had another light, to indicate the failure of the alternator failure light!" Most cars do. In fact, most any modern car has the same way to test the indicator lights. From engine-off, turn the key fully to the "driving"/engine-on position but don't engage the starter. I haven't seen a car where that didn't cause all of the dashboard indicator lights to turn on; that'll give you a pretty good hint if an indicator light isn't working. Please tell me you follow the manufacturer's (or, in applicable cases, operator's) predrive checklist before pushback or departure.

Yeah.  The light came on when you turned the key.  It just didn't come on when the alternator died.

@fluffysheap: At least in some automobiles, the alternator light bulb used to be a key part of the alternator circuit, such that a burned out bulb would cause the alternator to stop working; of course, the burned light bulb wouldn't light up to indicate that failure mode, so checking that the light illuminates when the engine isn't running would be important before setting out on a long trip.

@aCVn: Older cars had ammeters because they were simpler to design than a special circuit to detect the generator not working.

Dead battery = no go for me. Even if the battery is good, if the engine is hard to crank and not just cold, what if the engine stops in flight and is hard to restart?
I aborted a cross-country vacation in a rented 152 once because of a dead battery one leg into the vacation, went back, and spent a bummer Christmas at home, a decision I don't regret. (What I do regret is trying a "special VFR" approach to SJC on the way back and learning that 1 mile visibility isn't much visibility. Let's just say it was Christmas Day and SJC tower was very forgiving after I overshot the runway at 500 feet after getting clearance to land.)

First, don't go if you aren't prepared and comfortable with all aspects of the flight, so from that aspect you made a great decision. As you seem to already understand, the financial aspect shouldn't make even a small difference when it comes to making these decisions.
That being said, the main thing to consider is what happens if the alternator fails and the battery dies shortly thereafter: if the battery is weak, the margin of safety is reduced and this scenario is more likely than normal to develop, but by no means certain.  Even if it does happen, the POH will have abnormal and/or emergency procedures to follow.
Some things to consider when contemplating whether it is possible to safely fly in this scenario are whether you are:

flying an aircraft that doesn't rely on electricity for critical systems
flying in an area that requires certain surveillance or communication equipment (like a transponder or two-way communication)
flying under VFR (IFR requires equipment that could quit working)
are comfortable flying without electronic navigation assistance and communication radios (or have portable equipment that doesn't require ship power)
are comfortable with the additional risk that would be added on to everything else for the proposed flight

Consider the fact that some older airplanes don't even have an electrical system outside of the engine, and they fly just fine!  Again though, you need to be comfortable navigating using dead reckoning and without communication equipment if needed.

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Where is an EASA PPL valid outside of Europe?
I am considering obtaining an EASA PPL in the U.K. I would like to know where exactly in the world the license is recognized with little to no additional paperwork/training outside of Europe. Specifically I would like to know what is needed to fly in the Caribbean, Colombia or Chile with this license.
I am a complete aviation beginner so apologies if this is a silly question.

It might also depend on where the aircraft you intend to fly is registered.

In general: What is required for a pilot to fly in another country? Also related: May I fly an aircraft registered in an EASA member with an EASA licence (NOT same country as airplane) outside Europe?

This is probably related; at least in the Caribbean many GA aircraft are US-registered

Yes, the EASA PPL is valid worldwide, but you must check the local laws prior to fly, for example, here in Brazil to fly a Brazilian registrated airplane (PT-***) you shoud have an ANAC PPL license, but if you are flying to Brazil in an UK based Aircraft( reg. G-****), you can fly it with your EASA PPL.
If you intent to Fly a Non-European aircraft for a long period in a same country, you should validate your EASA license within the local Aviation Authority, that ensures that you get the same level of license as you have from EASA.


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What course should be taken to make estimated calculations?

(skyvector.com)
When I want to calculate the leg time from GIJ to CRL going along the airway J554, at say FL190, I know that I have to calculate the ground speed first, but in order to do that, should I take 082° magnetic course, 087° magnetic course (reciprocal of 267° from CRL), or should I enter in the CX-2 flight computer (Plan Leg) an average of them?

What I would normally do is to enter in the CX-2 flight computer the true course (calculated with a plotter) in order to get the ground speed; but I want to know if it is correct to get the true course by converting the known (shown on the chart) magnetic course by adding or subtracting to it the magnetic variation, whatever be the case.
In this case the magnetic variation around GIJ is 1W and the magnetic variation around CRL is 3W, so the true course of the GIJ - BENJO - CRL leg would be 81° and 84°, am I correct? Once again I get confused without knowing if I should take true course 81°, 84° or an average of both.
In the explanations given in the FAA book ATP Test Prep, relative to the nav questions in the performance chapter, the course to be taken, is sometimes the magnetic course that corresponds to the beginning of the leg, other times it is taken from the end of the leg and other times it is an average of the leg's initial and ending magnetic courses.

What do you have the winds aloft in? Usually in true headings, no?

Practically it should not matter, because you don't have the winds aloft accurate to a degree either.

I would calculate that leg in two segments.  From GIJ to BENJO flying a course of 082 magnetic (50 NM), thence from BENJO to CRL on a magnetic course 087 (79 NM).
In addition, the magnetic variation is only applicable to hand plotting an arbitrary course using the map's orientation as a reference; IFR charts list true magnetic courses on their airways for ease of reference.
After that, you just need the winds aloft and you're off to the races!

What is a “true magnetic course”? Given that “true course” is used to indicate course according to reference ellipsoid as opposed to magnetic course, saying “true magnetic” is confusing. And as far as I can tell, the numbers on the map (where adjacent to VORs) are radials, which used to correspond to magnetic headings but usually don't any more because the VORs are not periodically re-aligned to the changing magnetic declination.

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How many labels are defined in ARINC 429 for calibrated altitude?
How many labels are defined in ARINC 429 for calibrated altitude?

What Equipment ID are you interested in?

I dont know it.................

Are you trying to decode an ARINC label or figure out what label to send the data as or something else? By "calibrated" to mean baro corrected?

I find out what is the Arinc label for calibrated alt data?

In my copy of ARINC 429 (2004), there is no label defined for "calibrated altitude". There are labels defined for [Pressure] Altitude (1013.2 mbar) and Baro Corrected Altitude. What exactly are you trying to indicate?

There is no defined "calibrated altitude".
The following are all altitude related labels:

102 Selected Altitude,
107 Selected Cruise Altitude,
120 Range to Altitude,
127 Selected Landing Altitude,
131 Intruder Altitude,
144 Altitude Error,
153 Max Altitude,
162 Density Altitude,
164 Min Descent Altitude (MDA),
203 Altitude,
204 Baro Corrected Altitude #1 & Baro Altitude,
206 Altitude (Variable Resolution),
212 Altitude Rate,
220 Baro Corrected Altitude #2,
225 Compensated Altitude Rate,
251 Baro Corrected Altitude #3,
252 Baro Corrected Altitude #4,
254 Altitude Rate,
323 Geometric Altitude,
361 Altitude (Inertial)

In ARINC 429 a label refers to a parameter, for instance AOA (angle of attack). When you have several sensors for the same parameter, the same label is used for all sensors but 2 additional digits (SDI, Source Destination Identifier) are used to distinguish them, for instance left AOA and right AOA.
As a summary, a parameter can't use several labels but the same label might refer to similar parameters from different sources or sensors.


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What is the difference between ARINC 429 labels 025 and 102 for Selected Altitude?
What is the difference between ARINC 429 labels 025 and 102 for Selected Altitude?

According to A429, the difference is the type of data coding. Label 025 is BCD. Label 102 is BNR.
Label 025 by being a Binary Coded Decimal codes each character of the altitude value in binary. With a range of 0 to 50000 feet, the first digit uses 3 bits and the remaining use 4 bits each for total of 19 data bits.
Label 102 is a Binary number. The range is 0 to 65535. There are 16 data bits (2^16 = 65536).
Both are transmitted. Receivers will use the version most appropriate for the application.  BCD is normally used for display. BNR is normally used in computations.


text:
How to reduce the volume of the GTN750 traffic warning beep?
We've got a GTN 750 with ADS-B IN and OUT. When we encounter traffic it emits a high pitched pulsing beep. It cannot be muted by any means - say you are on final and there's an aircraft holding short but with an active transponder, it will beep like mad which is really distracting.
Is there a way to at least adjust the volume?
At half the volume it presently is at it would be bearable. We couldn't find any setting to effect that.

Have you contacted the manufacturer? That seems to be a likely place to start.

Yes. It's really hard to get a useful reply from Garmin.

There are numerous alert volume settings in the configuration pages of the GTN 750. Your local Garmin authorised dealer/installer should be able to identify the correct setting for the particular traffic system installed in your airplane.


text:
How can the wind speed and direction be calculated from on-board measurements?
I am currently learning C++ on my own in my spare time. I am writing a little application that will help me while at work.  I have come across a situation where I have some given values, but im not sure of the formula to use in order to render the end answer I am looking for.
Basically, I have the following parameters available to me:

Desired Track
Current Heading
Ground Speed
True Airspeed

I am interested in finding the wind speed and wind direction.
I have googled and googled for hours. Obviously most people use the old aviation E6B. However, that obviously doesn't work for programming. I was wondering if anyone happened to know, or know how I can find that formula.

I don't see any formulas on that website.  I did see some formulas on the wind triangle wiki page, but they are very vague and don't explain in detail what is going on.  Seems to be kind of difficult to explain mathematically.

There is a nice page of aviation formulas, that include wind triangles, here:  http://edwilliams.org/avform.htm

With the set of parameters available to you, you cannot do this.
If you have the actual track instead of the desired track, you will be able to calculate the wind.
The simplest way to do this is using vector math.
There are three vectors to consider:

ground speed vector $\vec{V_{gs}}$
air speed vector $\vec{V_{as}}  $
wind speed vector $\vec{V_{ws}}  $

$\vec{V_{gs}} =\vec{V_{as}} +  \vec{V_{ws}}  $
$\vec{V_{ws}} = \vec{V_{gs}}  - \vec{V_{as}}  $
I assume the actual track angle ($\phi$) and heading ($\psi$) are with respect to the true North.
The north component of your air speed is then: $V_{as} \cdot \cos(\psi)$ and the east component of your air speed is: $V_{as} \cdot \sin(\psi)$
For ground speed the decomposition is: north: $V_{gs} \cdot \cos(\phi)$ and the east component of your ground speed is: $V_{gs} \cdot \sin(\phi)$
$$\begin{bmatrix}
       V_{ws,north}\\
       V_{ws,east}
        \end{bmatrix} = \begin{bmatrix}
      V_{gs} \cdot \cos(\phi) -
      V_{as} \cdot \cos(\psi) \\
      V_{gs} \cdot \sin(\phi) -
      V_{as} \cdot \sin(\psi)        \end{bmatrix}$$
You now have the north and east component of the wind vector. This you can change to a speed and direction, but I leave that last part up to you. Don't forget that wind direction is usually reported as the direction from which the wind is coming.

To find the wind speed from the North and East components use the root of the sum of the squares:
$V_{ws}=\sqrt{V_{ws,north}^2 +
       V_{ws,east}
^2}$
The wind direction can be found by
$\tan^{-1} (\frac {V_{ws,north}}{V_{ws,east} }) $
Note that this will give a division by 0 for winds exactly from north or south.
To implement it in a computer language the atan2 function can be used. This prevents division by zero and also returns the direction of the full range of the circle instead of semi-circular
wind_dir = atan2(-wind_north, -wind_east)
This should give the direction from which the wind is coming in radians.

Thanks DeltaLima.  I actually have an available parameter of North and East wind component in the data.  Just had no clue about the reference.  Now I think I can figure it out.

For those of you in the future that may be wondering.

To find the wind speed = apply this formula WS=SQRT((x^2)+(y^2))
If it is in Meters per Second, be sure to convert to Knots if needed.
To find the wind direction = apply this formula WD=ATAN2(y,x) where Y == to North/South vector and the X == the East/West vector.  Once you run this formula, you will be presented with a degree in radian format.  Convert the Radian to degrees with this formula Degree= (Radian*180)/Pi
Finally, our last step is to take it from a Wind TO direction to a wind FROM direction (which is what aviation uses) to do that, simply add 180 degrees.

Hi Justin, great to see that you figured it out. Feel free to edit my answer to add your findings.

Just realised that you may not have enough reputation to edit my text. I'll add it myself. Welcome to the site!

Thanks!  Been a UAV pilot for years.  Just trying to make some simple E6B tools more applicable to what I do!


text:
How can I create a map of all paths of flights incoming to an airport in a given day?
Is there any where I could find a map overlaid with the paths of all flights that came into a given airport on a given day?
I've found a lot of maps that show the current location of all flights, or the path of a single flight, but I haven't been able to find any that have the paths of many flights at once.
I don't really want to scan through every flight manually, but if I could see all of their paths I could pick out the ones that have interesting tangents for further study.

Background: I recently moved in to an apartment near an airport. I enjoy watching the flights come in, but one of my new roommates is less thrilled. He remarks that some of the flights seem to be pointed directly at our building until their final turn, so if the pilots were somehow incapacitated, we'd be in trouble. I think that's geometrically incorrect, but would like to prove it.

If you could explain what you need this map for, it would be more clear exactly what sort of data you are looking for

For which airport?

@J.Hougaard I need the map so I can see if the planes are actually on a path directly as my building for a significant amount of time. (So, frivolity.) This was originally in my post, but was edited out of it.

@acpilot I'm interested in YTZ

What airport is  YTZ?

Toronto City Center

Depending on what you actually want to know, and how far from the airport you are, you may as well look at the standard arrivals and departures trajectories. In practical all aircraft  close to the airport use the same set of paths which are named STARs and SIDs. Indeed this needs some explanation as it's difficult to see where the paths are related to buildings, streets, etc. City Center seems to be a small airport, and most of the traffic is to/from Pearson.

Some visual information here for City Center.

I have written something like this for myself, see my answer here. However, it needs some basic knowledge about python. And it grabs the data right from flightradar24, I quess they don't like code being published to grab their data... However, I could do the job for you...

@mins Thanks, the illustrations in that document are very helpful! I didn't realize the landing paths were so specified. That's not quite as clear as an overhead map, but maybe I can use the identifiers from that document to find maps elsewhere.

@sweber That's very neat, more or less what I was hoping to find. It's too bad the data isn't openly easily available.

Your roommate realises there are 2 pilots at the controls, right?

Well you didn't state which airport you are interested in but obviously you only want data for a single airport.
You might want to look into a noise abatement reporting system. For instance, London Heathrow maintains the great website Webtrak (https://webtrak52.bksv.com/lhr4) to communicate with the pubic about changing SIDs, STARs and noise levels. (They already have much of the TMA over the heavily populated area, and they want to add another runway)

One option you have is to ask the airport for the data. They can deliver it to you in a shp-file that you can open with QGIS that is free software. With QGIS you can create maps and filter the radar tracks. All major airports often have a track monitoring system that saves data från the ATC-radar not from the ADS-B transponder. Usually the airport environmental department and the airport acoustics team/consultants have access to the historical flight track data.
Here are some examples of track monitoring systems that airports use
ANOMS
CASPER
TOPSONIC
FlightRadar24/FlightAwere etc. mostly consist of ADSB crowd input and is not fully reliable. Some airliners also send out the wrong position from their ADS-B transponder. That is called spoofing. To my knowledge FlightRadar24 only lets you export one path at a time.
You can also setup your own gear and record ADSB data with dump1090, that requires som skills, money and time.

Can you refine you answer... "ask the airport for the data": Which organization at the airport? How does the airport have the full actual flight data (not the flight plan)? "FR24 mostly consist of ADSB input": Don't they have agreements with ANSP to get their data too? "Some airliners also send out the wrong position from their ADS-B transponder": How can that happen? (isn't the ADS-B ground receiver the faulty link of the chain?) "setup your own gear and record ADSB data": How can you get the full flight path from a local DS-B?

Wait. You're saying there are airliners that are intentionally spoofing their location on ADS-B? Why?

I would also like to know that.

I would start with the approach charts for that airport, see if the flight paths are indeed over your housing, and at what altidude.
The gov't published approach charts are here
https://www.faa.gov/air_traffic/flight_info/aeronav/digital_products/dtpp/
There are also sites like this one that show "live" (likely delayed some number of minutes) tracks of aircraft currently airborne. You can zoom in and see if any tracks are over your housing.
This is the Boston, MA area for instance:
https://www.flightradar24.com/42.36,-71.01/7
And this one shows where they departed from and where they are landing
https://www.radarbox24.com/@42.47000,-71.26623,z14

You mention the arrival path before the final turn to the runway, known as the base leg on a visual approach. When cleared for a visual approach the pilot flies the base leg as near or far from the runway as he or she sees fit based on altitude, distance, obstructions, traffic to be followed.

Start with the FAA on-time dataset:
https://www.transtats.bts.gov/DL_SelectFields.asp
This is only for domestic flights but a good start.

Link doesn't work but from looking at the site I'm not sure where you would get the actual flight paths, just departure/arrival airports and times.


text:
How to find runway direction classification, code number and code letter?
I am creating a solution that generated the limitation surfaces for runways according to ICAO Annex 14. One of the parameters that I need is the runway directions classification, code number and code letter. But so far I only found one country that has this information in their AIPs.
Are there anyone who know this stuff enough, that would be able to provide some guidelines to how I could guess these information based on thresholds and declared distances etc?

Looking at three random AIP's (Denmark, Sweden, Norway), the aerodrome reference code is mentioned in all three (in the AD 2 text section). Which country are you having issues with exactly?

I've never heard the term "runway direction classification" before, and it is not mentioned in Annex 14 either. Are you sure you have the right name for it?

Didnt look in Sweden and norway documents yet, but was looking in UK AIPs. If you look in section 12 in the danish AIPs you will find Code letter, Code Number and Classification for each runway. Its PA_Cat 1 to 3 ect, NINST and NONP

"Runway direction" is from EuroControl AIXM format where a Runway is typical composed of two RunwayDirections.

Table 4-1. Dimensions and slopes of obstacle limitation surfaces — Approach runways

Cool. I was under the impression that runways also had a code used for these limitation surfaces.  I checked AIXM classes for the airport, though did not find this attribute there: https://ext.eurocontrol.int/aixmwiki_public/bin/view/AIXM/Class_AirportHeliport

Also, a danish airport has two different codes (EKYT) for their runways, ergo the code is not for the airport itself as it is different for those two runways. So I am confused by your argument

Each runway also has a code, otherwise you cant design the limitation surfaces for each runway. Lets say an airport has two runways, ofcause if one of them is large enough for a large airplane to land, then ofcause the airport reference code will also indicate this. But that dont mean that the large airplane can land at the other very small grass runway - and this also means that airports dont need to cut down trees for the grass runway just because large airplanes lands at the first runway. So for designing limitation surfaces, each runway has its own code.


text:
How do ADS-B and ADS-C get used on transoceanic flights?
I have three questions regarding ADS-B and ADS-C. (Hopefully you don't feel my questions are not related.)
(1) What's the scope of availability of ADS-B? Let's say an airliner equipped with all the necessary equipment for ADS-B in the US flies over to Tokyo. When or where does ADS-B stop working?
(2) I read from this post that ADS-C is used in some oceanic environments including the Pacific between certain flight levels. Roughly what percentage of transoceanic flights currently take advantage of the ADS-C system?
(3) I assume ADS-C is not a common transoceanic surveillance system, if it's true ADS-C is only used above certain flight levels. If so, what are alternatives to ADS-C? What other (surveillance) systems are being used to follow transoceanic flights? Self-reporting? GNSS? Or what?

1) ADS-B will stop working when the transponder is switched off at the gate after arrival in Tokyo. Airliners use the 1090 MHz Extended Squitter variety of ADS-B which is the worldwide standard.
2) I don't have hard numbers but I guess it is approximately 90 percent of the flights. At most economical cruise flight levels, ADS-C is mandatory.
3) ADS-C is a common system. For aircraft not equipped, position reporting of HF is the alternative. And soon space based ADS-B will be available as well.


text:
Are well-known IR AAMs 'compatible' with aircraft from other countries?
The AA-2 Atoll was a Russian reverse-engineered clone of the AIM-9B Sidewinder.  There are some sources that indicate, with varying degrees of veracity, that it was a good enough clone that the two could be used with the other side's aircraft (i.e. early MiGs launching Sidewinders and Western aircraft of that era launching Atolls).
However, the Russians have developed other short-range AAMs since then (Aphid, Archer), and the US has evolved the Sidewinder quite significantly from its humble roots as well.  In addition, other Western IR AAMs have been developed as well (such as the Israeli Python family).  This, along with the presence of mixed coalitions and even mixed air forces such as Malaysia's in this modern age, has me wondering: whose IR AAMs can be launched from whose planes?
More specifically:

Are current Russian jets (such as Flankers and Fulcrums) backwards compatible to the AA-2's electrical interface? (Bonus points if they can actually launch the AA-2 still.)
How backwards compatible are current Western jets (on external stores stations) to early Sidewinders, electrically speaking? (I know that some early Sidewinders required a cryobottle in the launch rail, we can ignore that for now.)
How forwards compatible are current Sidewinders to early Western jets? (i.e. could you launch an AIM-9M or an AIM-9X in analog mode off of an F-5 or A-4?)
Are other Western AAMs (such as the Israeli Python) compatible with the Sidewinder electrical interface?  (i.e. can a US F-16 hang a pair of Python-4 missiles off its wingtips and have them work "out of the box"?)
Last, and most of all, could you launch a modern Sidewinder (AIM-9L/M/P or AIM-9X in analog mode) from a Russian/Soviet jet (of any era, bonus points if it's one of the modern ones though), or have the interfaces diverged enough over the years to make that impossible?  Do the Malaysians need two stocks of IR-guided AAMs at all times, or could they get by on Sidewinders if they ran out of Archers or vice versa?

I edited your title a bit: when I first read it, I thought you were asking if any aircraft exist that can launch the missiles backwards or sideways :-)

@Pondlife  hmm...  that gives me an interesting idea!

The integration of weapons in an aircraft is based on four major issues.
The first issue is the mechanical compatibility: will the airplane break when you transport or fire the missile, because the missile is too heavy and/or is too powerful?
Typically, I don't think you can fire an AMRAAM from a P-51 Mustang....
This is a huge problem, but for the examples you give, the missiles are similar to each other so there is a great chance that both Sukhoi, Mig and McDonnell Douglas fighters have enough mechanical strength to transport and fire the missile. If there is not, you cannot do a lot of things to correct it, unless you change your airplane or your missile.
The second issue is about aerodynamics: will the missile, when fired, hit the airframe? It is likely the air flow around the airframe will create whirls which that might cause the missile to be pushed into the airframe.
This issue is often solved by studying how the missile will behave in the whirls of the aircraft, and by designing it to go away from the aircraft.
Note: you also don't want your air to air missile to go straight down, because it will lose the target. So this question of aerodynamics is always important
The third issue is about sensors: if you fire a missile, you first need to "tell" it what its target is. So you need to have sensors (or external sensors from which the aircraft has info by radio) in your aircraft.
By extension, you need to have the good sensors in your aircraft (the appropriate distance to use the full distance of the missile....). Again, for the modern fighters you mentioned, it will in general be OK. Even more if you're speaking of infrared missiles that don't have that much information before launching.
The fourth issue is electrical and electronic interfaces. In most of the cases, you can plug them in.
But you might have to adapt the current and tension on the electrical interfaces. On that point, you are lucky because the aircraft industry uses conventions of frequency for electrical current in order to have components with the smallest weight. So there is a good chance that Russian as well as Western jets have the same frequency of currents, and can adapt the tension and current.
On the electronic interface, you might have to change the missile launcher on the aircraft to have the correct plugs. I don't know how huge is it to change a missile launcher, but I guess that if it is possible for military people to do it, it takes at least a few hours.
To conclude, there is a high probability that all the missiles you mentioned are compatible with some industrial adaptations provided to the missile and/or the missile launcher, and some programming to do in the aircraft combat system. However, combining these missiles requires that the crew doing it knows in depth both the Western jet technology and the Russian missile technology.... which might be difficult in our political reality!

Can't compare the AIM-9 and AIM-120 here as their firing sequences are different. You're in fact more likely to successfully launch an AIM-120 from a P-51 than an AIM-9 as the AIM-120 only starts its engine after detaching from the launch rail while the AIM-9 starts its while still on the launch rail (all other things being equal, I'm not taking the electronics into account here obviously, only mechanical linkages) :)

On the other hand, the power needed for the radar of the missile might be prohibitive for the power available in a Mustang. Anyway, I was just giving this as an example that would be easily understandable


text:
Why isn't the course fixed along an airway?
Why does in some cases magnetic course (not magnetic variation) change between navaids along a same airway? Isn't it supposed that a straight line in an aeronautical chart representing an airway has always the same magnetic course between navaids? Apparently that isn't so, but I don't understand why isn't so.

Related: KLAX ✦ HDG 090° ✦ Cross the US ✦ Cross the Atlantic ✦ Which coast is that?

Thank you for your answer. I have to digest a little the answer, but in general terms I think I get it. I guess I didn't express myself clearly, so I posted a new question.
http://aviation.stackexchange.com/questions/29839/what-course-should-be-taken-to-make-estimated-calculations

To make it easier the course isn't fix along a airway because of earth convergency. As we know the if go from one meridian to another the direction of local north changes and because of this the direction of track also change.
As we know we fly great circle path this effect becomes more visible as distance between 2 points increase or change in longitude increases .
Formula for consideration =
convergency = Change in longitude * sin ( mean latitude)


text:
In what cases does an airplane return to airport?
I’m just wondering in what kind of emergency cases an airplane would return to the airport?
I am a programmer and security enthusiast — what kind of security issue should I have to find that would make the pilots consider it is a good idea to land and fix the security issue?

I'm not quite sure what you mean by a security issue. Do you mean a software security issue? If so, why are you probing for vulnerabilities on an aircraft currently in the air? Beyond that, physical security issues would really be handled on a case-by-case basis: bomb threats, weapons, and unruly passengers could all prompt an urgent landing.

@ZachLipton Yes, I mean software security (since I am a programmer). In such cases, how would a finding have to be reported?

Looking for security vulnerabilities on an airplane you're currently flying on as a passenger is always an extraordinarily bad idea, if not something that can land you in hot water with the authorities. There's no mechanism for this, and pilots are not knowledgeable about software security; if the plane does land because of this, it would be because they're suspicious of the strange passenger who keeps talking about a security issue. This work is done, on the ground, by researchers and vendors using systems they're authorized to access, not random passengers.

For example: United Airlines bug bounty program: "Attempting any of the following will result in permanent disqualification from the bug bounty program and possible criminal and/or legal investigation[...]Any testing on aircraft or aircraft systems such as inflight entertainment or inflight Wi-Fi"

It would be impossible to list all the possible emergencies that would make a pilot choose to land rather than continue a flight; it may be easier to list the ones that wouldn't cause them to want to land immediately. Pilots are a pretty paranoid bunch on average because the ones that aren't tend to die.
Regarding the specific word "return" in your answer, though, they would usually only return to the origin if that was the best option available at the time, which depends primarily on distance and altitude but would also be affected by winds, runway lengths and the exact nature of the problem.

"Pilots are a pretty paranoid bunch on average because the ones that aren't tend to die" or, at the very least, have a really difficult time explaining to their instructor or examiner why the action they took was the safest course of action available to them at the time.

Well that all depends on the nature of the need to return.
The short answer is:  anytime where, in the judgment of the flight crew, returning to the departure airport and landing presents the safest outcome for termination of the flight.
The choice of returning to the departure airport is driven by the nature of the emergency and the viability of other alternatives in solving the crisis.  It’s a pretty broad set of circumstances here.  There never is one single answer in ADM; some answers are better than others.


text:
How is a horizontal stabilizer attached to the fuselage and works as a trimmable Horizontal Tail as well?
I am trying to figure out how does the horizontal stab attached itself to the plane and moves up and down? Is the HS attached by the rear spar and to the fuselage?

You are going to have to clarify what aircraft you are talking about. In its most basic sense its attached much like the wings are, and moves up and down with a system of cables and pulleys or hydraulic actuators.

You might get a better response if you can explain what sort of answer you want. Are you asking how it's physically connected (e.g. bolts, screws, hinges)? And are you asking about a conventional horizontal stabilizer, or about a stabilator?

Fighter aircraft usually have their tailplane connected to the fuselage with a single pivot joint, as visible in this F-15 drawing:

Passenger aircraft often have a horizontal tailplane which is a single part, and as such, the entire stabilizer is being trimmed by an actuator around a pivot, as can be seen in this 727 drawing. The actuating system is different on newer aircraft, but the idea is the same.

The stabilizer is hinged at the quarter-chord point of the tail surface and has a second, movable attachment point. This second point can be moved up and down, generally by turning a spindle on which a nut rides which moves the second attachment point.

A300 stabilizer root (source)
On this picture (sorry, was the best I could find now) you see the stabilizer being attached to the bulkhead ahead of the APU. Ahead of it, near the left edge of the drawing, you see the vertical spindle which moves the forward attachment point. It turns according to trim commands from the flight control computer or from the cockpit.

Apart from those listed above, some unique aircraft have the horizontal stabilizer attached solid to the vertical stabilizer and then the entire pair pivots around a point on the empennage. The Lockheed Jetstar does this (next time you look at a Jetstar, look for the silver strip of metal below the horiz. stab.) but more commonly, the Mooney M20 series uses this mechanism, illustrated below:


text:
In order to become a pilot, should an individual have an above average mathematical ability?
I would very much like to become an airline pilot however maths has never been my strongest subject. Are most pilots mathematically adept or can I get away with being average?

Nowadays the only fields that really require good knowledge of math is mathematics. Everything else has computers do the calculations, meaning you only need 'normal' math abilities.

Today, most calculation work has been taken over by clever instruments. It cant' hurt, though, to develop the ability to quickly check if the result looks reasonable. But this is more experience than innate ability.

an average mathematical ability of a human is very low. If you randomly would select a human from a world population, there is a high chance that this person would not be able to solve a linear system of linear equations.

There is always tremendous confusion between mathematics and just arithmetic.  I'm guessing that sadly the OP means they are just plain bad at ordinary daily arithmetic.

@DavidGrinberg Mathmatics has almost nothing to do with calculations and many areas require lots of it: physics, computer science, anything concerning itself with statistics, which is almost every form of science.

@JensSchauder this is getting off topic for comments, but even in those fields you don't need much math. All the formulas already have programs to work out the actual math, you just need to know how to plug in the values and analyze the results. The only time you actually need to work out the math is either in school or if you are building one of those formulas

@DavidGrinberg this is a dangerous misconception. But yes this is way of topic

In short, no.
To quote Patrick Smith, veteran pilot and author of Cockpit Confidential and the blog  "Ask the Pilot,"

There's a lingering assumption that airline pilots are required to demonstrate some sort of Newtonian genius before every takeoff- a vestige, maybe, from the days when airmen carried slide rules and practiced celestial navigation...
  The basics are what pilots encounter. Routine arrival assignments require some quickie mental arithmetic.

So basically, it doesn't involve super complex math. You need to be able to do some moderate arithmetic and geometry, but nothing so complex that it can't be done, as Smith says, on

my $6.95 calculator from CVS- the one flight-bag accessory more indispensable than an emergency checklist, aircraft deicing guide, or a bag of ramen noodles.

Yep. Like accounting, you need a firm grounding in the basics, mostly high school stuff. If your math skills are terrible, flying is probably not for you, but if you can compute a fuel ratio, use a compass, and understand basic trig functions you will be fine.

One thing I'd note is that "Basic arithmetic and geometry" could be argued to be above average

the problem is: "compute a fuel ratio, use a compass, and understand basic trig functions".  In the USA, 99% of people would describe that skillset as: "Geeky!" "Top Expert!" "Incredibly good at mathematics!" "The genius kid".

Most people I've encountered who consider themselves "mathematically challenged" are stymied by the word "Mathematics" yet will easily calculate change on a purchase, or divide up a bill between diners. At worst, you've probably got a pretty detailed calculator on your phone!
When it comes to flying, it doesn't get much more complex than addition, subtraction multiplication and division for a very long while. The sort of maths you will need is "I'm flying at 95 Knots for 190 Nautical Miles, how long will this take me?" - division. or "I'm flying for 30 minutes and I'll burn 0.2L fuel per hour, how much fuel will I use" - multiplication. To labour a point - "my course is 120 degrees, but my wind correction angle is +3 degrees, what heading should I fly" - er, addition.
That final example is pertinent, there is an element of calculating some degrees of wind correction which is some proper trigonometry! Luckily you have tools (apps, slide rules) to calculate this part for you. As long as you understand what the app/calculator/slide rule is telling you in principal then you can use the tools at your disposal.
Beyond basic flying, yes, there is an element of more advanced mathematics. But maths is just like climbing stairs - one step at a time. You will find some "math" sort of stuff on exams later on.
Anecdotally, I have a good friend who is an airline pilot and he would be the first to admit he's not the best at the maths part of it. There you go.

The trouble is: what you describe in para 1 (change etc), it's unlikely 20% of adults in the US can do that. Para 2, I doubt 5% of adults in the US can do that. Para 3, hardly anyone can do that, other than a few professionals (and kids in junior high who barely-memorize-with-no-understanding what sin/cos is.)

Here are the sort of things you do frequently as a pilot that involve "Math" or even just "numbers":
The air traffic controller tells you, "One seven charlie, turn left three zero degrees, climb and maintain four thousand, squawk five seven three one."  If you are dyslexic, you might have problems remembering this string of numbers until you can use them.  But if your dyslexia is very mild, un-diagnosed, and not really noticeable, you probably can write the numbers down quickly on a notepad until you have time to accurately type them into your instruments.  Keep in mind that you are bouncing around in turbulence and tryng to hand-fly an airplane while you are doing this.
Your aircraft takes a bird strike while you are on the runway in the takeoff roll.  You immediately need to know if your airspeed (a number) is high enough for you to continue to climb with one engine; or whether you should shut everything down and stand on the brakes.  A commerical pilot will need to memorize about ten of these types of numbers, for every airplane that they flies, so that they can use them immediately in an emergency situation.  Captain Sully Sullenberger had to know instantly what his "best angle of glide speed" was when his engines failed, to glide as far as possible.  This is not "math" but it is memorization and quick recall of a number.  I personally do not like the newer glass-panel airspeed indicators because they are mostly just a number, not a clock-like needle on a dial.  With a needle on a dial (steam-gauge instrument), you don't really have to remember a number, you can just remember a position--where the needle on the dial is happy, and where it means danger.  Even a chimp can remember what territory is safe, and what territory is dangerous.  And when our brain gets oxygen deprived during emergency situations, we become chimps.  Numbers become garbage.
Here is more math:  You are given all the weights and positions (inches from a line on the fuselage) of people, luggage, and fuel.  You must do some arithmetic that adds some of these numbers and multiplies others, coming up with the placement of a dot on a chart (a weight and balance chart). If the dot is too high, the airplane is too heavy; if it is too far right, the airplane is loaded too far aft.  This is basic arithmetic and use of a graph.  And after you do it for a test manually, a computer does it for you always after that in real life.
So basically, if you can not memorize ten numbers and recall them quickly, and if you are bad at simple arithmetic story problems and basic graphing, they you will have trouble as a pilot.  But you do not need to know calculus, geometry, or advanced algebra.
However, I do not know your situation if you are overseas.  In the United States, you can get a private pilots license for less than the cost of a semester of college, and then build up your hours as a basic flight instructor.  Overseas, there may be more obstacles, in the way of aptitude testing, that I am not aware of the in the United States.

I'd have to check back what the exact accident was, but those needles (plural) are a known risk. The problem is that 9000 feet looks like "almost 10.000 feet plus 9000 feet" because multiple needles share a single dial.

@MSalters Though that isn't really an unsolvable problem. Just make the small-steps needle move continuously, and the large-steps needle move in quantized steps. That way it would become clear if you are looking at e.g. 0+9k or 10k+9k. Not asking why this isn't being done (that would be a separate question, and I suspect the answer would have a lot to do with plain old manufacturer inertia, warranted or otherwise), merely pointing out that it could be done that way and would mitigate the issue you raise in your comment.

@MichaelKjörling, actually, quantized steps make the problem worse, not better. It's like the clock—if the small hand moves continuously, five-to-twelve is unambiguous. But if the small hand jumped from 11 to 12 at once, then is it 5-to-11, or 5-to-12? Did it jump already or not?

Probably the most essential thing, based on 30 years experince, is the ability to recover your attention, situational awareness and invoke a personal calmness so that you can use what you do have between your ears - oh - and quickly, remember you are in a fast moving machine. Getting preoccupied and indecisive wastes precious time and will kill you, maybe others. So learn attention recovery before you start worrying about simple arithmetic. (Check out the pilots test on the Psyfactors website to see if you are there or what you need to be there.). It will also help you with the arithmetic.

I actually am a licensed commercial pilot, so I can comment.

you need to be comfortable doing simple calculations, like estimating time
you need to be able to memorize a fair amount, including the navaid frequencies
you need to be healthy and able to reach all the switches and rotate your neck
you need to be able to tolerate sleep disruptions
you need to be able to focus and have confidence in your training and abilities.


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Is it possible to re-engine aircraft with different engine options?
Most airliners have multiple engine options and so I was wondering if it would be possible for operators to fit a different engine type to their existing aircraft; let's take for instance the Boeing 747-400 fitted with RB211-524Gs. Could these be interchanged with PW4000s or GE CF6s or would the differing wing loadings require structural changes to be made?

Theoretically: probably yes, but it won't be easy / cheap. Different engines have different thrust, different pylons and even use different software to communicate with the aircraft (FADEC).


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Is it ever permissible to takeoff on an aircraft heavier than its MTOW?
I'm thinking in terms of the Concorde accident in 2000 having just read part of the report which states that they were in effect several tonnes heavier than they should of been factoring in the tailwind and tyre speed restriction imposed for that reason. The crew took 3 tonnes of taxi fuel of which they only burned 800kg and that put them at least a tonne above MTOW not taking the tailwind into consideration which the report states would have been negligible. So I was wondering, is there any margin for takeoffs with weights marginally higher than MTOW? (obviously in this case they were ridiculously heavy amongst a whole host of other poor decisions taken by the crew)

Yes, although that specific exemption might not be what you're thinking about

Military necessity. Sometimes called emergency war weight we could, with explicit permission, take off above max gross weight up to this EWW. And this: departing for Grenada, one pilot said 'we didn't know exactly what our weight was, but it was above EWW.`

The crew took 3 tonnes of taxi fuel of which they only burned 800kg and that put them at least a tonne above MTOW not taking the tailwind into consideration which the report states would have been negligible.

I can't speak to operations in today's environment, but at the two 747 carriers I worked for in the late 1980s and the 1990s, it was quite common to load more taxi fuel that you knew you would actually burn prior to takeoff. This was especially true for the 747-100, which had only a four bay center tank as opposed to the -200 which had a five bay center tank. Justification was easy. For example, if you were taxiing out at JFK to a trip to Tel Aviv, you well might burn 4000 lbs if you got caught in a line up. However, with any luck you'd get to the runway without delay, and you'd only burn 2000 (maybe even a little less), and you'd have the extra fuel for later. You wouldn't have the whole 2000 extra, because it would take about 20% of that to carry it.
Why was the extra fuel desirable? Well, in general as they say, the only time you have too much fuel is when you're on fire. Seriously, though, an extra 1500 to 2000 pounds could make the different between having to divert to Athens for fuel or going on to Tel Aviv.

So I was wondering, is there any margin for takeoffs with weights marginally higher than MTOW?

There is a practical margin but it's a judgement call as to how much it really is. If on the 747 all four engines stay running, the airplane will march right out, albeit with reduced performance, even if seriously overweight, but you've compromised the airplane's ability to stay in the air if an engine fails, especially if the failure is catastrophic.
Sometimes you're overloaded but don't know it. Either accidentally or on purpose the cargo weight you're carrying is misreported. The worst case that I experienced was taking a full cruise line crew and equipment from Miami to Trieste, where they would board a brand new cruise liner and put it in service.
We were at max gross and had enough fuel for that weight to reach Trieste. Once airborne at at cruise, we realized we were burning more fuel that we should. Using our mach number, altitude, and fuel flow we worked backward to find our weight and discovered we were somewhere between 30 and 35 thousand lbs heavier than we should have been. Our dispatch confirmed our calculations when we contacted them, and we made a fuel stop in Paris.
If you're flying freight, and pallets of uncovered dry goods are left out in the rain, they weight a lot more than when they were dry. That happened at Madras, India (now called Chennai) and that put us well over gross.
In a perfect world, neither experience should have happened. Welcome to the real world, at least as it existed in the 1990s.,

and still does, given that "standard weights" are used to calculate the combined weight of passengers and luggage. Which has caused crashes in the past of small commuter planes that were according to their loadsheets just under MTOW but in reality were seriously overloaded because the FAA/company mandates standard weights per piece of luggage or passenger were too low (decades old, not compensated for increased average weight of the population).

Actually, @757toga, "permissible" is in the question title. The question in the text is "is there margin for over MTOW take offs". So this answers the text, not the title.


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How could aerodynamicists reduce the intensity of the sonic boom?
My understanding of the sonic boom is that it is caused when shockwaves being emitted from an object travelling at Mach 1 or above compress and superimpose on each other because they cannot move out of the way fast enough causing an explosive release of sound energy. This was an issue throughout the gestation period of Concorde effectively halving its potential route network since no government would allow routine supersonic flight over populated areas. For a future SST are there any ways in which the effects of the boom could be curtailed somewhat?

NASA has some ideas about this: https://www.nasa.gov/feature/new-supersonic-technology-designed-to-reduce-sonic-booms

Related: https://aviation.stackexchange.com/questions/21870/is-there-a-boomless-sonic-technology-in-any-state-at-this-time


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What do FAA DERs require regarding low-level requirements in DO-178C?
Software developed for aircraft needing TA certification pretty much has to be done using a process following RTCA/DO-178C.  My question regards low-level (sometimes called "derived") requirements:
Low-level requirements either refine high-level requirements, or express design decisions.  I've been told a low-level requirement should be traceable to some statement or small block of code, and at DAL C and above, each piece of code needs to be traceable to a low-level requirement.
Do DERs want to see a test corresponding to each low-level requirement, or is that only so for the high-level requirements?  Would it be OK to do testing at a function level ("unit testing") as low-level requirement testing, and are the DERs happy with that?

DERs? what is it?

Design Engineering Representatives.  These are people who don't work for the FAA but are authorized by the FAA to guide a product through the safety assurance process. In practical terms, if the DER says you have to do something or supply a certain documentation, you have to do it or you won't be approved. The closest analogue in EASA to the DER is a Panel 10 Coordinator.

uhm, then I probably suggest to rephrase the question. As we do not sit in the head of a DER, we cannot know how they think or what they want, making this question slightly "opinion based". If you can formulate it so that you require only references to documentation or regulations, I think that it might be easier to answer.

Actually, @Federico, the question is about the current state of the (subjective) DERs' interpretation of the rules.  So it is not asking for the answerer's opinion, it is asking for an assessment of the opinions of the people whose opinions count (the DERs). One data point:  The consulting DER we have spoken to has said that the low-level requirements do have to be tested ("verified") even at DAL C.

That does not change much. Answerer's opinions or someone else's opinions, still opinions are. It will be more likely to receive an answer if you would ask "what rules/directives/documents the DER has to base its decision on".

One thing I would start with is that low level requirements are not the same as derived requirements, although low level requirements can be derived. Derived requirements are requirements that cannot be traced to a higher level requirement.
For verification of DO-178C Level C software, your SVCP will need to completely cover high level and low level requirements as well as attain 100% statement coverage of your code.
As far as what the DER for your project will approve, there really isn't any way for us to know.

I can't think of any better words that this to describe how the 178 objectives are satisfied, great answer. Higher level testing is preferred as it tests the software on the unit connected to real interfaces but where you can't get full condition/decision/statement coverage from High Level tests, you should supplement these with low level/unit tests.


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Why do some fighters have two engines?
Some countries (e.g. Russia) develop fighter aircraft (e.g. Sukhoi) with 2 engines.
Is it for maneuverability, or is it because they can't build an engine that would meet the power requirement?

Russia and sukhoi jets

Also, not all Russian fighters have two engines: MiG-21/23/27, SU-17 (to name a few) have a single engine.

The edit that added examples (#3) feels weird - it implies that Russian Sukhois are somewhat unusual in their twin engine configuration, which is not true.

The general purpose was redundancy. Splitting the power demand of the airframe and payload made for smaller engines and the ability to stay airborne and RTB (return to base) if one engine suffers a failure.

too broad. In some cases it's redundancy, in other cases it's the unavailability of a single engine with the required thrust. In yet other cases it's a matter of size (a single engine would be too big for the available space, 2 smaller ones side by side can be made to fit).

As pilots, we very often go right for the aerodynamic reasons, but one glaring reason has been omitted from the discussion - price.  Governments have to choose between having a smaller number of more expensive, likely more capable, aircraft and having a larger number of smaller, lighter, less expensive aircraft.  This applies not only to initial cost, but also to ongoing maintenance, parts and fuel cost to operate the aircraft.  The F-16 is a great example of an economically efficient aircraft that can be operated by nations on a budget due to its small size, single engine and availability of parts versus an engineering marvel like the F-22 which is no longer in production due in no small part to the difficulty of obtaining parts, a better explanation of which follows here:  https://www.defenceaviation.com/2016/05/why-did-the-united-states-stop-f-22-production-could-lockheed-martin-restart-the-production-line.html
Also, along economic lines, a quick visual price comparison is found here:  https://www.popularmechanics.com/military/weapons/news/a25678/the-cost-of-new-fighters-keeps-going-up-up-up/
Price issues aside, from a pilot's perspective I don't think there is a pilot alive who would not want a second engine for many reasons, but we aren't the ones buying the jets.

wrong on a lot of grounds. Pilots may not want a second engine because it means a larger, less agile, aircraft that's less survivable in a turning fight. You can see that when comparing the F-16 and F/A-18, the F-16 can turn a lot tighter than its larger brother.

Actually, correct on all grounds, not "wrong on a lot of grounds".  As I clearly stated in my answer, I was discussing the strategic objectives of a government and of a military agency, not the smaller perspective of the individual combatant.  And no, you don't have to give up an engine to have a great jet in a turning fight, the F-22 is a great example.  I have flown both single-engine and twin-engine supersonic military aircraft, including the F-16, Uncle Sam was kind enough to grant me a pair of silver wings after a lot of hard work.

Regarding the number of pilots that prefer two engines, there is a significant statistical bias: The selection of samples depends on what is measured. One could think it means that most pilots prefer twin engines, but it does not! It is just as possible that most pilots prefer to have one engine, but died because of that before the samples where chosen. (Quite an interesting example for statistical bias!)


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Why does TAWS alert depends on airspeed?
According to the TSO 151c:

Speed. Airspeed or groundspeed must be included in the logic that determines basic
  GPWS alerting time for “excessive closure rate to terrain” and “flight into terrain when not in
  landing configuration” to allow maximum time for the flight crew to react and take corrective
  action.

As I understand for "flight into terrain when not in landing configuration" modes, in the guides corner speeds are given as from 190 KTS to 250 KTS. I can understand the calculations dependency on airspeed but do you have any idea how these speeds are selected? Are they regulated by FAA or EASA? As far as i know,

§91.117   Aircraft speed.
  (a) Unless otherwise authorized by the Administrator, no person may operate an aircraft below 10,000 feet MSL at an indicated airspeed of more than 250 knots (288 m.p.h.).

but why 190 KTS? Is there any speed limits that should be obeyed for approaches and landing?

are we speaking of a specific aircraft model? where do those numbers (190/250 KTS) appear?

Distance to the terrain divided by the closure speed gives you the time it will take to reach the terrain. If you are 5 minutes away you don't need a warning.

@Federico I am not speaking about a specific aircraft, guides also says it can change accorrding to the aircraft type between 190-220 knots. I wonder is there any description what should be the IAS during approach and landing.

@GdD is 5 minutes sort of a standard? I could not find it in  FLTA given in TSO151.

@tigris, it was just a number I picked out of my head.

Most TAWS or EGPWS computers give a 60 second CAUTION TERRAIN and a 30 second TERRAIN, TERRAIN PULL UP warnings.

@wbeard52: That's the matter for a good formal answer...

@wbeard52 indeed i'd like to learn what are the speed limits for approach , final approach and landing for a standard airliner aircraft, like A380 or B737? If it is said that your speed limit should be 190 knots maximum for approach and 160 knots for final approach then it is ok for me. I wonder abouut those limits.


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Why is the reheat exhaust flame of some fighter aircraft blue while for some it is orange?
Why is the afterburner flame of some fighter aircraft blue while for some it is orange?

Nothing more than photography and ambient light (disregarding "exotic" fuels and designs).  Take a look at these images of Phantoms in reheat.  Sometimes it's yellow, sometimes it's white.

I am looking for the engine and fuel aspects, lighting and ambient lights make a very minuscule difference.

"lighting and ambient lights make a very minuscule difference".  On what do you base this statement?  Take two identical aircraft.  At night, the reheat plume appears more white.  During the day, it appears more yellow.  Since they are identical, I can think of no other reason.  It's certainly the case with Phantoms, on which I worked for 4 years.  You can clearly see this in the images I linked.  Here are some more examples.

Please post the sources of your images

I took the time to find some very representative images.  Compare this one with this one.  Same engine, same fuel.

Forget jet engines, just look at the lit tip of a cigarette in the day and the night. Same fuel, same cigarette, very different colour

Simon and Jamiec please see the reheat of Sukhoi 30 during day anf night. It is blue by day as well as by night , and I have seen this at takeoff during day and night from a very close distance.

I agree with Simon's comments. Lighting and ambient lights make all the difference.
The flame is always equally bright, so if the ambient light is lower, the difference between the flame and the rest of the image is larger. When the difference exceeds the dynamic range of the film or sensor, the image of the flame becomes saturated in all channels and ends up as white. Note, that all the images with white flame are night ones.
Also the blue sensor is slightly sensitive to near infrared (being about half wavelength of the blue light), so when high sensitivity/long time are used, this causes the blue glow around the white flames on night images, while on day images with lower sensitivity it is not noticeable.

About the sensor: they are all sensitive to IR, and its a common practice to use a camera to check an IR remote control.  If it's working, the LED flashes blueish white like the exhaust flames in the picture. Also, cigarettes and glowing coal appears in this color. So yes, hot glowing stuff often appears blueish white on photos. But many better cameras have an IR filter and give a more realistic picture.

If anyone has any doubt about Jan's answer, go ask at Photo.SE, they'll give you more detail than you could ever want.


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Why are the minima for Cat A higher than for other categories at KSEA ILS 16L?
I was looking at the KSEA ILS 16L approach (depicted below) and was wondering just why the minima are bumped up for Cat A aircraft (64 feet on both DA and HAT, as well as 200 feet of RVR).  Thing is, I've already checked Chapter 10 of the TERPS, and nothing in there says anything about approach-category-specific adjustments to ILS minima, nor does the Form 8260 for this approach say anything about the cause.  (This also makes the SA CAT I and CAT II/III procedures Cat A NA, which matters for aircraft that have a small aircraft CAT II ILS authorization IAW FSIMS 4.2.3.)  Furthermore, neither 16C nor 16R's ILS approaches have this feature, which is even stranger because you'd think that 16L and 16C are close enough together that their ILS OCSes would overlap, and they also use highly similar MAPs (climb to 900 on a heading, then intercept the SEA 161 radial, then proceed to TEBNE along that radial -- the only difference is the initial heading of 160 for 16C vs 165 for 16L).

What is doing this? Is there an obstacle there that is doing this only to small aircraft?  Is there some vagary of the TERPS I'm not finding? Is this an error?

The higher DA will drive the higher required VIS, since you're farther from the runway at 264 ATDZE on glideslope than you are at 200' ATDZE on glideslope.  The interesting question is, what drives the higher DA for Cat A... no guess there.  Very curious!

I haven't looked at the TERPS for this one (and, following the Gunnison, CO, question, I'm no longer positive that I'd understand what I'm looking for), but in your Q you only mention approach info (ILS OCSes, etc.)... don't forget that missed approach information is also part of the minima determination. Did you continue your TERPS search beyond the approach side, and examine the MAPs as well? I don't know if the MAPs are different for each rwy, but if they go in different directions, then maybe there is an obstacle on the south side somewhere that is more specific to CatA?

@Jimmy TERPS Chapter 10 also covers the ILS MAP as well as the approach itself -- I will admit I mostly skimmed it looking for things that'd change with approach category.  The MAP for 16C is very similar to 16L, though, as the only change is the heading of 165 on 16L vs 160 on 16C to intercept the SEA 161 radial to TEBNE.

I'm guessing that it's very closely related to the reasons here:  http://aviation.stackexchange.com/q/35236/69

@Lnafziger -- thing is, 8260.58A does not apply to an ILS approach AFAICT. Furthermore, the logic behind that answer can only forbid Cat A approaches, not raise the minima for Cat A alone

What makes this even more illogical is that most light planes can try the approach at the 1800 RVR mark simply by flying a less-flap or no-flap approach and landing (which they're likely to do anyway considering the traffic mix and runway length)

@UnrecognizedFallingObject I get that it doesn't apply, but there are probably similar requirements for other types of approaches and if they have to go missed from a higher altitude then it basically accomplishes a higher climb gradient on the missed. The other example probably just could raise it enough to matter so they just prohibited it while this one just needed a small adjustment.  (Again, I'm just guessing but it seems reasonable....)

The minima's are usually decided based on the Missed Approach procedure, which one of the criteria being obstacle clearance. I believe the answer lies in your question, its due to the heading course and altitude restriction on the MAP point. RWY 16L needs to climb straight 165 deg which puts you through the obstacle , whereas 16R Missed approach procedure heading can clear the '464' obstacle. . In either case Obstacle driving the change, Having CAT A with the lower speed in the heading of 165 deg it won't get you clear the obstacle. The PBN approaches are even marked higher for all aircraft type which can be inferred from other terminal charts.

Yes, but how does speed impact climb performance?

Yeah, why would this obstacle only affect Cat A minima?

If you look at the perfomance stats listed here you find that all aircraft with a climb rate of 1000 ft/min or less are all cat A. All cat B aircraft have a climb rate of 1000 ft/min or more. The slower the Vref generally the lower the climb rate. They have to make the mins to be safe for any cat A aircraft that could be equipped. So if somebody shows up in an Aerona Chief that's been fitted with ILS equip they have to be able to clear obstacles with a 360 ft/min climb rate.

@TomMcW clarified the question of why its affecting only CAT A minima.

Karthik - Oh, I was responding to UFO @Steve Kuo's question. I forgot to tag them. Also forgot to +1. Done :)